Using less then 57% HI in RP

[borolithium]

My dreams have involved a source of HI that only has a density of 1.62. 10 Litres are used for every 10 pounds of ephed. The yields are a consistent 50%. I will not post my whole procedure, as it has been posted many times by many other bees, and after several wacker oxidations, reductive aminations, and the like, this procedure is childs play.

Now it is clear to me that this acid needs to be dehydrated. The search engine has brought up many possibilities including:

1. Dehydrate the acid with dry HCL gas. This procedure works excellent for dehydrating hydrobromic acid for the conversion of safrole to bromosafrole, although some chlorosafrole is produced as a by-product. Since I have a cylinder of dry HCL gas for doing my crystallizing, this would be the most convenient if indeed it worked

2. Distilling the HI until the steam reaches 126C. This would work fine, although some HI would be lost in the first bit of distillate. It is also the slowest way to go

3. Adding GAA or a mix of hypophosphoric acid and iodine. Sounds interesting, but i don't have any of these right now. I could round up some GAA easy enough, but is it worth it?

So another thing I am wondering is if the use of this weaker acid, somewhere around 50% I gather, would result in the relatively poor yield? Or would it simply result in a higher concentration of by product in the end product? (iodoephedrine, unconverted ephedrine, etc)

[Rhodium]

So another thing I am wondering is if the use of this weaker acid, somewhere around 50% I gather, would result in the relatively poor yield? Or would it simply result in a higher concentration of by product in the end product?

The iodination of ephedrine to iodoephedrine is going to be less inhibited than the subsequent reduction of iodoephedrine to methamphetamine by the use of too weak acid, so yes, an increased amount of half-reacted intermediate products like iodoephedrine is to be expected.

[SHORTY]

Personally if i wanted to get 57%HI from 50%HI i would just leave  the condenser off until the boiling point reached 126-127C (with adequate ventilation of course) and then put the condenser back on and reflux. 

Of course the proper way would bee to distill it off as you mentioned but unless i needed alot then I would bee too lazy to do that for a small amount.

[Rhodium]

Naturally, you mean 126-127°C.

[spectralshift]

>>The iodination of ephedrine to iodoephedrine is going to be less inhibited than the subsequent reduction of iodoephedrine to methamphetamine by the use of too weak acid, so yes, an increased amount of half-reacted intermediate products like iodoephedrine is to be expected.


Swim can confirm that..well he suspected it from a result.

thin h3po3 was used instead of a wax h3po3.
no water was added, because the h3po3 contained AT LEAST 1:1 water to h3po3 already.

in addition, the temperature probably only reached 90C in the large test tube that was used. for about 6hr.


the small amount of product was entirely tweaky, just horrible. lip licking constantly, sore mouth, jaw spasms, from the outset, the first lick of the plate.

[xtaldoc]

This is a problem that SWIX has had to deal with in the past on some larger rxns, due to the fact that HI was available to me (in bulk) only in an approximately 48% sol'n.  For Bees purposes, Swix found it best to simply add the calculated amount of Iodine (plus a bit extra RP)to this weaker acid prior to the rxn.  This workaround always brought Swix results identical to the results obtained via 57% HI.  I'm in sort of a rush at the moment, but I hope this helps. BTW, when considering the 'actual' effective concentration of HI optimal for H-I-P reductive dehydroxylations, Swix reminds himself to always visualize the rxn process, as a whole.  The side reaction of forming HI from RP & Iodine involves the consumption of water; thereby causing an actual rise in the concentration of HI in solution (in a wet rxn).  The side reaction involving the conversion of pfed-HCL to pfed-HI (or pfed-base to pfed-HI) has the effect of lowering the actual concentration of HI in  the rxn mixture. These events are only a sample of the whole picture, but I'm hoping that it illustrates my method of visualizing these things and might shed some light for others.

[ragnaroekk]

After all I read and all my personal experience is the iodination the difficult and limited step - the reduction of the iodinated (pseudo)ephedrine is relativly easy as long HI is present.
Ref. Gattermann-Wieland 42ed. and others.

For dehydration of the HI 100% H3PO4 - crystalline phosphoric acid may be used as this is much easier than gassing with HCl and at least the same effective - perhaps more. Add the phosphoric in parts over some time, not to drive out the HI and loose it, add until white fog starts appearing over the surface - then stop and add later more.

The low yields are explainable by this mechanism:
As long as the concentration of the HI is high enough (pseudo)ephedrine is iodinated and IMMEDIATLY reduced by the HI present. So each iodination/reduction costs two HI molecules and concentration of the HI sinks rapidly below the limit necessary for the iodination - the amount HI present would sufficice to reduce iodinated pfed, but there is none more formed - so fini.
Try the H3PO4 - 100% - it will work and also reduce reaction times and allow lower temperatures.

A question to Rhodium:
Why is never iodinated ephedrine/pseudo found in streetmeth? If this would be found only in traces some forensic whores would have sung us the song of its dangers (see the chlorinated compound) in some longwinded articles already, thats for sure.

sorry to say: your first post is plain misinforming.

RaGnARoEkK

[Rhodium]

Ref. Gattermann-Wieland 42ed. and others.

Please don't unspecifically refer to huge reference works, please take your time to scan and/or type the pertinent parts, as well as tell us on exactly what page in which edition you found the information. I do that myself when I want to prove something, or just help/teach other people for that matter.

A question to Rhodium:
Why is never iodinated ephedrine/pseudo found in streetmeth? If this would be found only in traces some forensic whores would have sung us the song of its dangers (see the chlorinated compound) in some longwinded articles already, thats for sure.

It's because iodoephedrine is very reactive, and very easily cyclizes to the aziridine (well-known impurity), eliminates HI to form P2P methylimine (which further hydrolyzes to P2P, another well-known impurity), as well as other degradation products and/or condensation products formed by any combination between these in turn. I've posted a lot of articles on this topic (do you want specific links?).

[ragnaroekk]

and if you want four to be five - it may be this way.


who knows?
perhaps four IS five?

RaGnArOEkK

[Osmium]

> After all I read and all my personal experience is the
> iodination the difficult and limited step

Read an organic chemistry book for beginners. The benzylic position is very reactive in nucleophilic substitution reactions. Benzyl alcohols react with HX in the cold! All it takes to convert benzyl alcohol to benzyl chloride is shaking the former with strong aq. HCl for a few minutes.

> who knows? perhaps four IS five?

Perhaps somebody needs to work on his counting skills.

[ragnaroekk]

Benzylalcohol reacts in the cold - but not all benzylic alcohols. A longer chain - in special if substituted and steric hinderance can make the easy substitution to a rather hard task.
You may read a basic chemistry book on this or try to substitute ephedrine with HCl in the cold - even in the heat you get - my god its true! - only some ephedrine/pseudoephedrine mixture and no chlorinated ephedrine.

This "read a basic chem-book" style is a universal weapon to make others look stupid. No argument. I give this back to you with ease as I am sure it is longer ago that you read such a book than I.

have a nice day
RaGNaRoEkK

[Osmium]

We can discuss this all day long, and wonder if SN2 nucleophilic substitution will predominate or rather SN1 nucleophilic substitution since pseudo is a secondary benzylic alcohol. Comparing HCl and HI is equally useless since HI happens to be a stronger acid and a much better nucleophile.
The reduction of the iodo-intermediate still happens to be the rate determining step since every factor that slows down the iodination part of the reaction (like steric hindrance) will equally affect this second step.

Can you show us a ref where the reduction of a iodoalkane with HI is fast at room temperature? I doubt you can.

[ragnaroekk]

But I can show you a hundred references telling HI being one of the strongest reducing agents known in chemistry and also telling that iodine makes the best leaving group of all halogens.

btw. I dont get the sense of your question - do you iodinate (pseudo)ephedrine at roomtemperature with HI? In serious amounts is understood, not 3% or so.....

And we wont forget that YOU started with HCl and benzylalcohol, Osmium, not me, YOU started to compare uncomparable processes, ok?
And talking about uncomparable things:
The halogenation deals with an hydroxyl group on the alpha carbon, the reduction deals with an iodine on the same place - tell me this makes no difference and make me laugh.

RaGNaRoeKk

[Osmium]

Ok, whatever you say. You are right and I am wrong. Have a good day.

[Rhodium]

a hundred references telling HI being one of the strongest reducing agents known in chemistry

Strong does not equal fast. "Strong" only implies "a potential to affect a wide range of functionalities", and does not give any information about the reaction taking 30 seconds or a week, only that the reaction is able to take place using that reagent, given time to do so.

[borolithium]

Thanks for the input. What I have available to me at this exact moment however, is dry hcl. I am going to give this a shot tonight on a micro batch and i will report my findings. There is likely a large percentage of iodoephedrine present, as the acetone wash causes a visible loss in yield.

dry gassing hcl is not at all difficult and the fact that it is well below freezing where i am, makes it even easier.

I am curious to see if this works, as there have been previous posts regarding dry hcl gassing that have been blasted to hell. One thing is for certain, it sure works great for dehydrating HBr in a bromosafrole reaction.

[ragnaroekk]

fast and hot reaction which is predominantly used here where I live. (sorry I didnt invent nor propagate it....) Nevertheless I can testify that such a reaction can produce 80%+ yields of pure product in very short time. (molar yield after steamdistillation/recrystallization). Not to talk about the immense waste of iodine and red phosphorus and the mindspoiling product if not recrystallized what isnt done usually here (ppl here actually prefer the impure variation, they call it "strong") this shows IMHO that iodinated ephedrine is very quick reduced by HI. The iodination proceeds fast by PI3 and the reduction by HI is almost faster - dont flame me, I cant help it, but the cooks here dont reflux at all, they let the flask sit and cool down whilst they proceed the next batch, what comes to 20 to 30 minutes hot reaction + 1 hour sit and cool.
All reagents incl. ephedrine labgrade. RP/I2/H3PO4-85%/ephedrine (ratios are a secret not known to me, for sure a LARGE excess of I2/RP is used).

But the point is: I have seen it fast in good yields of cleaned product.
And Jacked and Worlock and Geezmeister and many more will be able to back this up if they want to.

RaGNArOeKk